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<a name="boost_asio.reference.AsyncRandomAccessReadDevice"></a><a class="link" href="AsyncRandomAccessReadDevice.html" title="Buffer-oriented asynchronous random-access read device requirements">Buffer-oriented
      asynchronous random-access read device requirements</a>
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<p>
        In the table below, <code class="computeroutput">a</code> denotes an asynchronous random access
        read device object, <code class="computeroutput">o</code> denotes an offset of type <code class="computeroutput">boost::uint64_t</code>,
        <code class="computeroutput">mb</code> denotes an object satisfying <a class="link" href="MutableBufferSequence.html" title="Mutable buffer sequence requirements">mutable
        buffer sequence</a> requirements, and <code class="computeroutput">h</code> denotes an object
        satisfying <a class="link" href="ReadHandler.html" title="Read handler requirements">read handler</a>
        requirements.
      </p>
<div class="table">
<a name="boost_asio.reference.AsyncRandomAccessReadDevice.t0"></a><p class="title"><b>Table 4. Buffer-oriented asynchronous random-access read device requirements</b></p>
<div class="table-contents"><table class="table" summary="Buffer-oriented asynchronous random-access read device requirements">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  operation
                </p>
              </th>
<th>
                <p>
                  type
                </p>
              </th>
<th>
                <p>
                  semantics, pre/post-conditions
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <code class="computeroutput">a.get_executor()</code>
                </p>
              </td>
<td>
                <p>
                  A type satisfying the <a class="link" href="Executor1.html" title="Executor requirements">Executor
                  requirements</a>.
                </p>
              </td>
<td>
                <p>
                  Returns the associated I/O executor.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="computeroutput">a.async_read_some_at(o, mb, h);</code>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput">void</code>
                </p>
              </td>
<td>
                <p>
                  Initiates an asynchronous operation to read one or more bytes of
                  data from the device <code class="computeroutput">a</code> at the offset <code class="computeroutput">o</code>.
                  The operation is performed via the <code class="computeroutput">io_service</code> object
                  <code class="computeroutput">a.get_io_service()</code> and behaves according to <a class="link" href="asynchronous_operations.html" title="Requirements on asynchronous operations">asynchronous
                  operation</a> requirements.<br> <br> The mutable buffer
                  sequence <code class="computeroutput">mb</code> specifies memory where the data should
                  be placed. The <code class="computeroutput">async_read_some_at</code> operation shall
                  always fill a buffer in the sequence completely before proceeding
                  to the next.<br> <br> The implementation shall maintain one
                  or more copies of <code class="computeroutput">mb</code> until such time as the read operation
                  no longer requires access to the memory specified by the buffers
                  in the sequence. The program must ensure the memory is valid until:<br>
                  <br> — the last copy of <code class="computeroutput">mb</code> is destroyed, or<br>
                  <br> — the handler for the asynchronous read operation is invoked,<br>
                  <br> whichever comes first.<br> <br> If the total size of
                  all buffers in the sequence <code class="computeroutput">mb</code> is <code class="computeroutput">0</code>,
                  the asynchronous read operation shall complete immediately and
                  pass <code class="computeroutput">0</code> as the argument to the handler that specifies
                  the number of bytes read.
                </p>
              </td>
</tr>
</tbody>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2021 Christopher
      M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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